Blueberry Jam 4.000

Deb Lindsey for The Washington Post

Canning Canning Class Aug 6, 2014

Blueberry jam is one of the more foolproof preserves to make. The berries have so much natural pectin in their skin that the jam will thicken easily with no added pectin. Make sure to crush at least two-thirds of the berries with a sturdy potato masher.

Taste the berries before starting. If they are very tart, add more sugar. If they are very sweet, use less -- but use no less than 3 cups.

Make Ahead: The uncooked berries need to macerate for 1 hour. The sealed jam jars can be stored in a cool, dark place for up to 1 year. Refrigerate after opening.

4 half-pint jars

When you scale a recipe, keep in mind that cooking times and temperatures, pan sizes and seasonings may be affected, so adjust accordingly. Also, amounts listed in the directions will not reflect the changes made to ingredient amounts.

Tested size: 4 half-pint jars

  • 2 pints fresh blueberries, picked over for stems
  • 3 to 4 cups sugar, depending on the berry (see headnote)
  • Juice of 1 lemon
  • 4 sprigs lemon verbena, 1/2 teaspoon lemon zest or 1/4 teaspoon almond extract (optional)

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Rinse the berries. Spread them in a single layer on a clean kitchen towel until dry.

Combine the berries, sugar (as needed) and lemon juice in a mixing bowl. Add the lemon verbena or lemon zest, if using. Stir to blend well, then let the mixture sit at room temperature for 1 hour.

Transfer the mixture to a heavy-bottomed, nonreactive saucepan; discard the lemon verbena, if using. Use a potato masher to crush half of the berries, then stir to incorporate. Bring to a boil over high heat; cook long enough so the mixture foams, continuing to stir and mash all but a few of the berries.

When the mixture begins to gel at the bottom of the pan, you’re close to finished. Once the foam is almost entirely gone, the jam will be done (about 35 minutes). Test the set (see NOTES); stir in the almond extract, if using. Ladle the jam into the clean jars, leaving 1/2 inch of head space.

Clean the rim of each jar. Secure the warmed lids and finger tighten the rings (not too tightly). Process in the boiling water bath for 10 minutes (see NOTES). Use the jar lifter to transfer the jars to a clean, folded dish towel to cool for several hours.

Label and date the sealed jars.

NOTES: Water-bath canning safely seals high-acid, low-pH foods in jars. The time for processing in the water bath is calculated based on the size of the jar and the consistency and density of the food. For safety's sake, do not alter the jar size, ingredients, ratios or processing time in any canning recipe. If moved to change any of those factors, simply put the prepared food in the refrigerator and eat within a week.

There are three ways to test the set. The sheeting test suggests stirring the preserves, then lifting the spoon to watch the jam sheet off the spoon, flowing slowly and collecting along the bottom of the spoon before languidly dripping back into the pot. It looks like jam, not like syrup. The sheeting test takes a practiced eye.

The cold plate test is a surefire method of testing the set. Before beginning to cook the jam, tuck 3 small plates and 3 spoons into the freezer. Once the preserves seems to be set, use the cold spoon to place a tablespoon or so of jam on the plate. It will set instantly. Press against the blob of jam. Does it resist just a bit? Wrinkle a little? It’s done.

The third method is the lazy man’s cold plate test. Remove the preserves from the heat and cool for 3 to 5 minutes. Press against the surface of the jam. Does it resist just a bit? Wrinkle a little, as though a very small pebble has hit the surface of a pond? The jam is ready. If it is not yet set, put the preserves back on the stove, cook for 2 to 5 minutes at a strong, hard, foamy boil that rises up no matter how much you stir, then test again. Stop and start the cooking process as many times as necessary until satisfied with the set. The jam will set further as it sits, so err on the side of a loose set vs. a very firm set.

Fill a large canning kettle or deep stockpot two-thirds full with water. To keep the jars from rattling against the pot, place a rack in the pot. (A cake rack works well; a folded dish towel is equally effective.) Sanitize the jars in a short dishwasher cycle or by boiling them in a canning kettle or pot for 10 minutes. Fill a small saucepan with water and add the rings. Bring to a boil over high heat, slip in the lids and turn off the heat.

Use a jar lifter or tongs to lower the filled, sealed jars into the boiling water bath, keeping them upright. When all of the jars are in place, the water should be 1 to 2 inches above the jar tops. Add water as needed. Bring the water to a low boil before starting the timer for processing.

At the end of processing, turn off the heat and let the jars sit in the water bath until the boiling has stopped. That will reduce siphoning, in which the food burbles up under the lid, breaking the seal. Use the jar lifter or tongs to transfer the jars to a folded towel, keeping them upright. Leave the jars until they have completely cooled, at least 12 hours. Remove the rings and test the seal by lifting each jar by the lid. The lid should hold fast. Label and store in a cool, dry, dark space.

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Recipe Source

From Cathy Barrow, author of "Mrs. Wheelbarrow’s Practical Pantry: Recipes and Techniques for Year-Round Preserving" (Norton, November 2014).

Tested by Cathy Barrow.

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